$-\dfrac{5}{8} + \dfrac{7}{2} = {?}$
Answer: $ = - {\dfrac{5 \times 1}{8 \times 1}} + {\dfrac{7 \times 4}{2 \times 4}} $ $ = - {\dfrac{5}{8}} + {\dfrac{28}{8}} $ $ = - \dfrac{{5} + {28}}{8} $ $ = \dfrac{23}{8}$